1. Field of the Invention
The present invention relates to a circuit structural body provided with a combination of a bus-bar which constitutes a power circuit and a printed circuit board for controlling drive of a semiconductor switching element provided in the power circuit, and a method of manufacturing the same.
2. Description of the Related Art
In the related art, as means for distributing electric power to the respective electronic units from a common vehicle-mounted power source, an electric connection box in which a power distributing circuit formed by laminating a plurality of bus-bar boards is provided and a fuse and a relay switch are built in the circuit is generally known.
In addition, in order to realize downsizing of such electric connection box and high-speed switching control, a structure in which a semiconductor switching element such as FET is interposed between an input terminal and an output terminal in stead of the relay has been developed in recent years.
For example, JP-A-10-35375 discloses an electric connection box including a bus-bar board forming a current circuit, a FET as a semiconductor switching element to be built in the current circuit, and a printed circuit board for controlling operation of the FET. In this electric connection box, the bus-bar board and the printed circuit board are disposed in two levels on the upper side and the lower side at a distance apart from each other, and the FET is interposed between the two. A drain terminal and a source terminal of the FET are connected to the bus-bar board, and a gate terminal of the FET is connected to the printed circuit board.
In the electric connection box disclosed in JP-A-10-35375, at least two boards, that is, the bus-bar board and the printed circuit board, are necessary, and in addition, it is necessary to secure enough space for disposing these boards three dimensionally at a distance apart from each other and disposing the FET between these boards. Therefore, although a relay-type electric connection box in the related art may be downsized by introducing the FET, the entire structure is too complicated to realize sufficient downsizing and, in particular, reduction of the height continues to be an important task.
Since the FET is interposed between the bus-bar board and the printed circuit board in the electric connection box, heat generated by the FET is liable to stay between these boards, and thus a complicated structure must be employed for heat dissipation.
In addition, in the electric connection box, since the drain terminal and the source terminal of the FET is connected to the bus-bar board on the lower side, and the gate terminal is connected to the printed circuit board on the upper side, assembly of the entire electric connection box is complicated, and thus automatization is difficult. Therefore, improvement of such problems is demanded.